The present invention relates generally to an improved printing apparatus or composing system, and more particularly, to an improved printing apparatus or composing system of the type having a printing station, a printing force resisting means, an image carrier, a font element with a raised character positionable in printing alignment with the printing station and an improved means for exerting a printing force against the raised character on the font element to transfer an image thereof to the image carrier.
The printing apparatus or composing system of the present invention has particular application in the printing of relatively large characters for use in engineering drawing title blocks, flip charts, overhead transparencies, posters, silk screen stencils, signs, newspaper headlines, etc. These characters are generally much larger than most typewriters or other conventional means can generate. In the prior art, four major methods have been used to create such letters: stencils, press-on letters, photo typesetters and dry lettering printing processes. The application of stencils and press-on letters to form words and sentences is relatively time consuming. In addition, it is easy to misalign letters and get uneven spacing. Photo typesetting systems are rather large, expensive, permanent installations having several chemical baths that must be maintained. Further, a trained operator is necessary to get good results. Although the dry lettering processes presently used overcome many of the disadvantages and limitations of stencils, press-on letters and photo typesetters, a relatively large printing force is necessary to transfer an image of the desired character from the high-carbon content toners to the image carrier. Generally, the quality of the printing or the image transfer is dependent upon the magnitude of the printing force developed.
In prior art lettering systems, a variety of printing force exerting means have been utilized. One such means involves the use of a printing piston having a flat upper surface disposed in printing relationship with a printing surface. Such printing piston is lifted by a cam element, thereby creating a printing force to transfer an image of the character on the font element to the image carrier. Such a force exerting means is shown in U.S. pending patent application Ser. No. 622,715, filed Oct. 15, 1975. A primary disadvantage of this particular means is due to the fact that the force exerting surface is flat. Because of this, the forces which must be exerted against the printing surface are quite large, thus necessarily requiring a relatively powerful motor or drive means or complicated and space consuming mechanical advantage means.
Accordingly, there is a real need for an improved force exerting means usable in a dry lettering printing process which requires a minimum amount of force to create the necessary printing force and which is yet reasonably compact and free of extensive mechanical advantage means.